list.hpp

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#pragma once
 
/// @file userver/ydb/io/list.hpp
/// @brief YDB list container serialization traits
 
#include <ydb-cpp-sdk/client/value/value.h>
 
#include <iterator>
#include <ranges>
#include <type_traits>
#include <vector>  // for InsertRow
 
#include <userver/utils/assert.hpp>
#include <userver/utils/meta.hpp>
 
#include <userver/ydb/io/generic_optional.hpp>
#include <userver/ydb/io/traits.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace ydb {
 
namespace impl {
 
template <typename T>
class ParseItemsIterator final {
public:
    using difference_type = std::ptrdiff_t;
    using value_type = T;
    using reference = T;
    using iterator_category = std::input_iterator_tag;
 
    ParseItemsIterator() = default;
 
    ParseItemsIterator(NYdb::TValueParser& parser, const ParseContext& context)
        : parser_(&parser),
          context_(&context)
    {
        ++*this;
    }
 
    // Trivially copyable.
    ParseItemsIterator(const ParseItemsIterator&) = default;
    ParseItemsIterator& operator=(const ParseItemsIterator&) = default;
 
    T operator*() const {
        UASSERT(parser_ && context_);
        return ydb::Parse<T>(*parser_, *context_);
    }
 
    ParseItemsIterator& operator++() {
        UASSERT(parser_ && context_);
        if (!parser_->TryNextListItem()) {
            parser_ = nullptr;
        }
        return *this;
    }
 
    ParseItemsIterator operator++(int) {
        ParseItemsIterator copy{*this};
        ++*this;
        return copy;
    }
 
    bool operator==(const ParseItemsIterator& other) const noexcept {
        UASSERT(parser_ == nullptr || other.parser_ == nullptr);
        return parser_ == other.parser_;
    }
 
private:
    NYdb::TValueParser* parser_{nullptr};
    const ParseContext* context_{nullptr};
};
 
}  // namespace impl
 
/// @cond
struct InsertColumn;
using InsertRow = std::vector<InsertColumn>;
/// @endcond
 
template <typename T>
requires meta::kIsRange<T> && (!meta::kIsMap<T>)
struct ValueTraits<T> {
    using ValueType = meta::RangeValueType<T>;
 
    static T Parse(NYdb::TValueParser& parser, const ParseContext& context) {
        parser.OpenList();
#if __cpp_lib_ranges_to_container >= 202202L
        T result =
            std::ranges::subrange{
                impl::ParseItemsIterator<ValueType>{parser, context},
                impl::ParseItemsIterator<ValueType>{},
            } |
            std::ranges::to<T>();
#else
        T result(impl::ParseItemsIterator<ValueType>{parser, context}, impl::ParseItemsIterator<ValueType>{});
#endif
        parser.CloseList();
        return result;
    }
 
    template <typename Builder, typename U = const T&>
    static void Write(NYdb::TValueBuilderBase<Builder>& builder, U&& value) {
        bool list_opened = false;
        for (auto&& item : value) {
            if (!list_opened) {
                builder.BeginList();
                list_opened = true;
            }
            builder.AddListItem();
            ydb::Write(builder, item);
        }
        if (list_opened) {
            builder.EndList();
        } else if constexpr (std::is_same_v<ValueType, InsertRow>) {
            // Legacy behavior. Sometimes YDB will throw here due to insufficient type
            // info.
            builder.EmptyList();
        } else {
            builder.EmptyList(ValueTraits<ValueType>::MakeType());
        }
    }
 
    static NYdb::TType MakeType() {
        NYdb::TTypeBuilder builder;
        builder.List(ValueTraits<ValueType>::MakeType());
        return builder.Build();
    }
};
 
template <typename T>
requires meta::kIsRange<T> && (!meta::kIsMap<T>)
struct ValueTraits<std::optional<T>> : impl::GenericOptionalValueTraits<T> {};
 
}  // namespace ydb
 
USERVER_NAMESPACE_END